Water drainage devices are used in subsurface applications such as against foundation walls, at the edges of highways, and at the bases of civil engineering structures for removing water from subadjacent soil while "filtering" or preventing movement of soil particles therefrom. Such devices are typically rollable panels or "mats" which, when installed against a foundation wall, function to channel the water to a drainage pipe or sewer.
Drainage structures are typically fabricated using a three-dimensional core sheet having a corrugated profile with grooves therein, such as shown in U.S. Pat. No. 3,654,765 of Healy et al.; or a flat sheet having finger-like projections therefrom, such as shown in U.S. Pat. No. 4,057,500 of Wager or U.S. Pat. No. 4,572,700 of Mantarro et al.
Complex procedures for the continuous molding of core sheets are taught in U.S. Pat. No. 3,507,010 of Doleman et al. (grass-like blades) and U.S. Pat. No. 4,572,700 of Mantarro et al. (finger-like hollow cylinders) wherein revolving drum molds are used for forming the members that project outwards from the core sheet. A woven or nonwoven material, commonly called a "geotextile," is either adhered to or wrapped around the core. Thus, the core structure provides a conduit for the passage of water, while the geotextile prevents soil from entering and clogging the water conduit passages.
U.S. Pat. No. 4,840,515 of Freese and U.S. Pat. No. 4,943,185 of McGucken et al. disclose drainage units comprising a cuspated core sheet having frusto-conical projections to which are adhered a water-permeable soil filter fabric.
McGucken teaches that the drainage unit can be used in combination with a self-sealing waterproofing material which purportedly prevents water from reaching the exterior surface of the foundation wall.
The prior art drainage devices which employ hollow projections, such as the inverted frusto-conical sections taught by Freese and McGucken, are discovered by the present inventors to be incompatible when used in combination with soft waterproofing membranes or waterproofing materials. The present inventors have discovered at least two types of incompatibility between conventional drainage mats and waterproofing membranes arising sometimes after soil is backfilled against a drainage mat/waterproofing membrane that has been installed on the subterranean surface. In the first case, wherein the waterproofing membrane includes a plastic carrier sheet and adhesive layer, it is discovered by the present inventors that the carrier sheet deforms into the hollow frusto-conical projections overtime, thereby jeopardizing the integrity of the waterproofing membrane. The strain placed by soil pressures causes the sheet to deform, i.e. bulge into the backs of the cones, and to burst. In the second case, which may involve waterproofing membranes comprising soft waterproofing materials alone (e.g. rubberized asphalt, polyurethanes, etc.) or in combination with plastic carrier sheets, it is also discovered that the drainage mat exerts point-pressures which penetrate and/or displace the soft underlying waterproofing material, such that the drainage core comes into direct contact with the foundation wall or other subterranean surface. The integrity of the waterproofing material is thereby destroyed.
In view of the foregoing disadvantages of the prior art, a novel drainage device is needed.